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Old 09-13-2017, 08:42 PM   #1
WurlyBird
 
Join Date: Jan 2013
Location: North Pole, Alaska
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Default Vortex Generator position VG

If this has been discussed before I couldn't find it in the search function. I would like to call on everyone that has, or has had, VGs to give a report of their model, how far from the leading edge they positioned their VG, and what change they had. This may provide some empirical data to help others in the decision making process. I'm gonna do it, I just don't want to go through the flight testing process if it's already been done by others.
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Old 09-13-2017, 10:13 PM   #2
Dusty
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Default Re: Vortex Generator position VG

One vg's supplier (stolspeed?)has a testimonial section,a kf flyer tried staggered installation which he seems to think works.
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Old 09-13-2017, 10:55 PM   #3
jiott
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Default Re: Vortex Generator position VG

Try the search function again. Quite a lot of stuff comes up if you use the words: VG's or vortex generators in the keyword box and search Titles only (advanced search function). This subject has been rolled around a lot.
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Old 09-13-2017, 11:10 PM   #4
WurlyBird
 
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Default Re: Vortex Generator position VG

At the risk of being an ass, I followed your suggestion and searched "titles only" for "VG", "VG's", and "Vortex generators" and only two threads came up. One about what material to make some DIY ones out of and this one. I know VGs are discussed, A LOT, but I can not find much info about KF specific placement. Some people report miracles and other a waste of money, it comes down placement and having a collection of placement on each model and the results could be very useful. Maybe even helping fix issues with those reporting the wasted money.
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Old 09-13-2017, 11:20 PM   #5
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Default Re: Vortex Generator position VG

As an admission of inaccuracy, I had searched for "vortex generator". I went back and searched for "vortex generatorS" and four more threads popped up. Only one made mention of measurements and it was for only one model.
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Old 09-14-2017, 02:08 AM   #6
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Default Re: Vortex Generator position VG

Do try Stolspeed, they are Australian based. Very reasonably priced and the website shows quite a lot of data on tests that they conducted.
Good luck.
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Old 09-14-2017, 07:13 AM   #7
tx_swordguy
 
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Default Re: Vortex Generator position VG

I fly an avid flyer with a heavy hauler wing so my mileage may vary. I bought my VGs from land shorter.com due to price more than anything. I placed them 10% back from the leading edge and spaced roughly 2" I believe. Not saying it is a miracle but I am definitely a believer. I will state my performance changes and let you judge whether it is worth it to you. For me it was. My stall went from 40ish to 37ish no noted change in top end. prior to VGs my landings when approaching the flair my wings would rock back and forth as they were losing lift ( at least that is what they felt like) Now the wings are rock steady all the way to the ground and it has given me much more confidence in slipping over the power lines to land on my 1000' grass runway. That in and of itself is why I am so in favor of them for no other reason. To me the stall difference is not a big enough change to worry about but it did change. I also put VG on the underside of my horizontal stab approx 1" apart not sure I really noticed much more pitch authority but I do get a warm and fuzzy feeling and would probably do that again anyway. As far as cleaning the wing to me just wipe front to back with a wet rag and I don't have problems cleaning. Hope this helps a bit
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Old 09-14-2017, 09:15 AM   #8
WurlyBird
 
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Default Re: Vortex Generator position VG

Thank you for the feedback. I had not read the STOLspeed site. I like their information. Vortex-generators.com also has good descriptions as well as the best prices and an option for rectangular VGs like the ones BigJohn used on his KF that he reported on so well. I would like to go with landshorter.com just because they are the only one made in the US, but as is always the case they are not only the most expensive but you also need to supply your own adhesive and I like the idea of laser cut adhesive strips. But that is all brand stuff, which is not what this thread is about.

STOLspeed describes the location as being the highest point in the airfoil at a stall AOA. All other math aside, I want my plane to stall with the tail wheel in contact with the ground and the mains just off. So the VGs should be just forward of the highest point as the plane sits in parking, right? Is there a flaw with this conclusion I'm not seeing? Can anyone verify with their plane if placement works out like this?
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Old 09-14-2017, 09:45 AM   #9
trentp
 
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Default Re: Vortex Generator position VG

I spoke with a man at Oshkosh who essentially invented VGs as we know them today for increasing performance (prior to him they were used by the military as "engineering bandaids"), Jerry Burr. He has done tons of testing with VGs at every different location on his wing and he said he found the sweet spot to be at about 4% of the chord. He didn't seem to think there was any huge loss with mounting them too far forward however if you mount them too far back they can end up being blanketed by the separated boundary layer of air at high AOA (like at stall or during landing) and be rendered essentially ineffective. I asked him why most manufacturers suggest 10% of the chord for placement and he said he had no idea, and that he can let them do whatever they want and watch them scratch their heads as to how he lands so much slower than them.

I did have VGs on my standard wing that were about 10% back from the leading edge, they were on there when I bought it but the previous owner told me they didn't do much. On the STI wing I went ahead and placed them at about 4% and they seemed to have a pretty solid improvement. The plane is much more stable at slow speeds and it definitely stalls a little slower. It's insane the AOA that I can hang on the wing at. Overall I am happy with them and would definitely recommend them.

I used the STOLspeed VGs, they are nice because they are clear, are taped on instead of glued (you can remove them if you don't like them) and they are cheap
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Old 09-14-2017, 12:37 PM   #10
tx_swordguy
 
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Default Re: Vortex Generator position VG

I am no engineer so take it for what its worth, but I don't think the a visual mark is going to be the proper place to use (highest point sitting) As Trent says too far back you will loose the boundry layer before the VGs have a chance to "stick the air to the wing" It may even disrupt the air even more and exagerate the stall but that is just me thinking here. Each airfoil is slightly different and the wing may have a different high point. I think in general the VGs are placed before the high point to ensure the air adheres to the wing to keep the lift. What ever you do I would not try to out think the VG engineers.
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